This invention relates to a radiation-detecting device applied to computed radiation tomography (hereinafter abbreviated as CT).
An X-ray CT device of the third or fourth generation comprises a plurality of X-ray detectors arranged along the periphery. The detector involves a plurality of detection elements densely arranged in a direction. To obtain a CT image having a high resolving power, the detection elements have to be arranged with as short a pitch as possible. To meet this requirement, a solid scintillation detector constructed by combining a scintillator and photodiode is applied in place of the conventional gas ionization box.
With the conventional solid scintillation detector, a plurality of photodiode elements are mounted on a semiconductor substrate. A scintillation element is attached to the surface of each of the photodiode elements by means of a transparent adhesive. A collimator plate is set between the respective scintillation elements and also on the outside of the scintillation elements fixed at both ends of said scintillation element group. Thus, each scintillation element is sandwiched between two adjacent collimator plates. The conventional solid scintillation detectors constructed as described above are arranged at a small distance from each other along the periphery of the subject radiation-detecting device.
X-rays are brought into the conventional radiation detector at various angles, and the X-rays carried into the respective scintillation elements are detected with the sensitivity which varies with their incidence angles. The conventional radiation detector has the drawback that the manner in which the sensitivity of detecting the X-rays brought into the scintillators set at both ends of their group varies with the incidence angles of said X-rays is different from that in which the sensitivity of detecting the X-rays carried into the other scintillators varies with the incidence angles of said other X-rays. This undesirable event is assumed to arise from the undermentioned fact. Namely, the scintillation elements set at both ends of their group receive X-rays brought not only directly but also through the adjacent scintillation elements and free space (air region). In contrast, the other scintillation elements only receive directly introduced X-rays and those carried through the adjacent scintillation elements. Therefore, the two outermost scintillation elements receive a larger amount of X-rays than the other scintillation elements. Therefore, the scintillation elements provided at both ends of their group detect X-rays with a higher sensitivity than the other scintillation elements.
If, therefore, the X-ray detecting sensitivity differs as described above between the scintillation elements provided at both ends of their group and the other scintillation elements, then difficulties will be encountered in compensating the collected data, thus resulting in a failure to carry out an accurate diagnosis. The aforementioned difference in the X-ray detecting sensitivity between both groups of scintillation elements is also governed by the magnitude of a clearance allowed between the respective scintillation elements. If, therefore, an X-ray detector is set at a place different from that which was originally prescribed, then the X-ray detecting sensitivity will undesirably decrease.